Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
An actuator is a type of motor that is configured to move or control a mechanism or system. Typically, an actuator is controlled by an energy source, such as electric current, hydraulic fluid pressure, or pneumatic pressure, which the actuator in turn converts to motion. By way of example, an electric motor may convert electrical energy to mechanical torque. Similarly, a pneumatic actuator may convert energy formed by compressed air at high pressure into either linear or rotary motion, and a hydraulic piston may use hydraulic power to facilitate mechanical operation.
Some robotic devices use actuators to transform an electric signal into motion. If an actuator of a robotic device (robot actuator) experiences an electrical or mechanical failure, and this failure is not detected, the robot actuator may continue to operate, potentially causing injury to the robot or its environment. For this reason, robot actuators are often instrumented with a number of sensors, whose outputs may be used to evaluate the performance of the robot actuator. While some failure modes can be detected utilizing the sensors on the robot, this detection may not be robust, as a robot sensor itself may also fail. The use of redundant sensors can alleviate this issue; however, redundant sensors may add unwanted costs. Redundant sensors also tend to fail in the same way, so a redundant pair of sensors may fail at the same time.